Radial lead seal assembly for a generator and a radial lead seal assembly of a generator

ABSTRACT

A retrofit method for modifying a radial lead seal assembly of a generator and a radial lead seal assembly of a generator are presented. The radial lead seal assembly seals a radial chamber from an axial chamber. The radial lead seal assembly includes sealing elements disposed around a radial lead to seal an annular space between the radial lead and the radial chamber, a coil spring disposed around the radial lead between the sealing elements and a junction between the radial lead and the axial lead, and a nut. The retrofit method includes removing one or more of the sealing elements to define a radial space between the remainder of the sealing elements and the coil spring. Conical springs are inserted in the radial space and only partially compressed under a radially inward compressive load exerted on the radial lead seal assembly via the nut.

FIELD

Aspects of the present invention relate to generators, and in particularto a radial lead seal assembly in a generator.

DESCRIPTION OF RELATED ART

An electrical generator comprises a lead assembly to provide a fieldcurrent from an excitation source to a rotor winding. The lead assemblycomprises an axial lead and a radial lead. The axial lead extends withinan axial chamber through a rotor. The radial lead extends radiallyoutward from the axial lead through a radial chamber toward an outerdiameter of a rotor of the generator.

For generators used in nuclear power plants, the outer diameter of therotor may be subject to gas, typically hydrogen gas. Any leakage at theradial lead may allow the pressurized hydrogen gas to leak into theaxial lead chamber of the rotor. The leakage may be communicated fromthe axial lead chamber into an excitation system and atmosphere. Thishydrogen gas loss from the generator may require operations to maintaina proper operating pressure of the generator and may create a potentialhazardous condition if sufficient accumulation occurs.

A radial lead seal assembly is used in a generator to fluidically sealthe radial chamber from the axial chamber. A radial lead seal assemblymay include seal elements around the radial lead to seal an annularspace between the radial lead and the radial chamber. A currently useddesign is to spring load the radial lead assembly with a coil spring tocompensate material creep and relaxation of the seal elements afterassembly and operation.

The use of a coil spring is intended to keep the radial lead assemblyunder load after relaxation due to seal material creep and compressionset. The coil spring design, however, does not have a resisting forceapplied by a spanner nut torque and therefore bottoms out under a smallfraction of full spanner nut torque. With a small amount of relaxation,a large amount of the assembly force is lost. Because of the weak loadof the coil spring, the assembly load increases from an addedcentrifugal force of the coil spring at operating speed of thegenerator. This may result in a cycling of load on the radial leadassembly from standstill to operating speed of almost 50% higher whenoperating than at standstill. As a consequence, the radial lead assemblymay become under loaded at standstill and leak.

An improved radial lead seal assembly may require replacing the coilspring. However, due to the assembly's limited access and a height ofthe coil spring physical exceeding an available space for removal, aremoval of the coil spring in an existing radial lead seal assembly mayinvolve partial removal of winding component of the generator to providethe required accessibility to remove the coil spring, which entailsincreased effort and cost on the field.

SUMMARY

Briefly described, aspects of the present invention relate to a retrofitmethod for modifying a radial lead seal assembly of a generator and aradial lead seal assembly of a generator.

According to an aspect, a retrofit method is presented for modifying aradial lead seal assembly of a generator. The generator comprises a leadassembly for conducting a field current to a rotor winding. The leadassembly comprises an axial lead extending within an axial chamberthrough the rotor and a radial lead extending radially outward from theaxial lead through a radial chamber. The radial lead seal assemblyfluidically seals the radial chamber from the axial chamber. The radiallead seal assembly comprises a plurality of annular sealing elementsdisposed around the radial lead so as to seal an annular space betweenthe radial lead and the radial chamber, a coil spring disposed annularlyaround the radial lead between the plurality of sealing elements and ajunction between the radial lead and the axial lead, and a loadingmember. The retrofit method comprises removing one or more of theannular sealing elements to define a radial space between the remainderof the sealing elements and the coil spring. A plurality of conicalsprings is inserted in said radial space. A radially inward compressiveload is applied on the radial lead seal assembly via the loading membersuch that the conical springs are only partially compressed.

According to another aspect, a radial lead seal assembly of a generatoris presented. The generator comprises a lead assembly for conducting afield current to a rotor winding. The lead assembly comprises an axiallead extending within an axial chamber through the rotor and a radiallead extending radially outward from the axial lead through a radialchamber. The radial lead seal assembly comprises a plurality of annularsealing elements disposed around the radial lead to seal an annularspace between the radial lead and the radial chamber and thereby sealthe axial chamber fluidically from the radial chamber. A coil spring isdisposed annularly around the radial lead between the plurality ofsealing elements and a junction between the radial lead and the axiallead. A plurality of conical springs is disposed annularly around theradial lead in a radial gap between the plurality of sealing elementsand the coil spring. The radial lead seal assembly comprises a loadingmember for exerting a compressive load on the radial lead seal assemblyin a radially inward direction such that the conical springs are onlypartially compressed.

Various aspects and embodiments of the application as described aboveand hereinafter may not only be used in the combinations explicitlydescribed, but also in other combinations. Modifications will occur tothe skilled person upon reading and understanding of the description.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the application are explained in further detailwith respect to the accompanying drawings. In the drawings:

FIG. 1 illustrates a perspective cross section view of a lead assemblyof a generator according to an embodiment;

FIG. 2 illustrates a perspective view of an existing configuration of aradial lead seal assembly according to an embodiment;

FIG. 3 illustrates a perspective view of a modified configuration of aradial lead seal assembly according to an embodiment;

FIG. 4 illustrates a perspective view of a conical spring according toan embodiment;

FIG. 5 illustrates a perspective view of conical springs oriented in aseries configuration according to an embodiment;

FIG. 6 illustrates a perspective view of conical springs oriented in aparallel configuration according to an embodiment; and

FIG. 7 illustrates a perspective view of conical springs oriented in acombination of series and parallel configurations according to anembodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION OF INVENTION

A detailed description related to aspects of the present invention isdescribed hereafter with respect to the accompanying figures.

FIG. 1 illustrates a perspective view of a lead assembly 200 of agenerator according to an embodiment. According to the illustratedembodiment, the lead assembly 200 comprises an axial lead 300 extendingin an axial direction of a rotor 100 of the generator and a radial lead400 branching out radially outwardly from the axial lead 300. To thisend, the rotor 100 is provided with an axial chamber 320 and a radialchamber 420 connected to and extending radially outward from the axialchamber 320. The axial lead 300 and the radial lead 400 are respectivelypositioned with the axial chamber 320 and the radial chamber 420 of therotor 100. The lead assembly 200 is arranged to conduct a field currentfrom an excitation source (not shown) via the axial lead 300 and theradial lead 400 to a radially outward located rotor winding (not shown).

An outer diameter of a rotor 100 may be in contact with a pressurizedgas, such as hydrogen gas. Any gas leakage at the radial lead 400 mayallow hydrogen gas to be lost by leaking into the axial lead chamber 320of the rotor 100. The leakage may be communicated down through the axiallead chamber 320 into the excitation source and atmosphere. The hydrogengas loss may require operations to maintain a proper operating pressureof the generator. The leakage may create a potential hazardous conditionif sufficient accumulation occurs. A radial lead seal assembly is usedto prevent the gas leakage at the radial lead 400, as describedhereinafter.

FIG. 2 illustrates a perspective view of an assembly known type of aradial lead seal. As shown, the radial lead seal assembly 500 comprisesa plurality of annular sealing elements 510. The annular sealingelements 510 are disposed around the radial lead 400 so as to seal anannular space between a radial lead 400 and a radial chamber 420. Theannular sealing elements 510 may be made, for example of a materialcomprising neoprene rubber.

The radial lead seal assembly 500 shown in FIG. 2 comprises a coilspring 520 disposed annularly around the radial lead 400 between theplurality of sealing elements 510 and a junction 530 between the radiallead 400 and an axial lead 300. A nut 540 is engaged to a radially outerend of the radial lead 400. A torque is usually applied to the nut toexert a radially compressive load on the radial lead seal assembly 500.The radial lead seal assembly 500 may comprise a spacer 550 and a topwasher 560 disposed annularly around the radial lead 400 between the nut540 and the annular sealing elements 510. The radial lead seal assembly500 may comprise a bottom washer 570 disposed annularly around theradial lead 400 between the annular sealing elements 510 and the coilspring 520.

The compressive load applied by the torque on the nut 540 may fullycompress the coil spring 520. When fully compressed, the coil spring 520exerts a predetermined compressive load on the sealing elements 510,which cannot be changed or removed on the field due to spaceconstraints. The fully compressed travel of the coil spring 520 requiredfor this compressive load controls an amount of relaxation of the radiallead seal assembly 500 due to creep that may be accommodated with somedegree of retained loading by the coil spring 520. The fully compressedtravel of the coil spring 520 is not adjustable.

In the radial lead seal assembly 500 shown in FIG. 2, the coil spring520 does not have the resisting force to balance the compressive loadapplied by the torque on the nut 540. For example, the coil spring 520may be compressed to its maximum extent (i.e. bottoms out) under only afraction of the full torque applied on the nut 540. As a consequence,the configuration shown in FIG. 2 cannot maintain sufficient compressiveloading to the radial lead seal assembly 500 over a period of operationdue to material creep of seal elements 510 with thermal and compressionset. Because of a weak loading of the coil spring 520, a loading on theradial lead seal assembly 500 may increase from an added centrifugalforce of the coil spring 520 at operating speed of the generator. Thismay result in a cycling of load on the radial lead assembly 500 fromstandstill to operating speed of almost 50% higher when operating thanat standstill. As a result, the radial lead seal assembly 500 may becomeunder loaded at standstill and leak.

A solution to improve a performance of an existing configuration of aradial lead seal assembly 500 would be to replace the coil spring 520with an improved method of load retention. However, because of availablespace constraints, removal of the coil spring 520 would involve partialremoval of a winding component of the generator to provide the requiredaccessibility. Replacing the coil spring 520 in the existingconfiguration of the radial lead seal assembly 500 would thereforecreate costly forced and maintenance outages with poor customersatisfaction. In an example, the height of a coil spring 520 in a radiallead seal assembly 500 is about 2.2″ in the radial direction. In thisexample, the available removal distance for repairing a radial lead sealassembly 500 would be about 1.7″. The current solution to address a gasleakage issue through a radial lead assembly 500 is to replace theradial lead assembly 500 only without any modification to improve aperformance of the radial lead seal assembly 500.

FIG. 3 illustrates a perspective view of a modified configuration of aradial lead seal assembly 600 according to an embodiment of theinvention. The modified configuration of a radial lead seal assembly 600shown in FIG. 3 provides an improved sealing performance in relation tothe existing configuration of a radial lead seal assembly 500 shown inFIG. 2. This is achieved by providing one or more conical springs 620 toaugment the compressive force of the coil spring 510. As shown in FIG.3, the conical springs 620 are arranged radially between the coil spring520 and the sealing elements 510. The inventive configuration providesthat under a compressive load from a loading member, which in thisexample is a nut 540, the conical springs 620 do not bottom out but areonly partially compressed. This would provide a sufficient compressiveloading on the radial lead seal assembly 600 to better compensate forthe relaxation of the sealing elements 510 due to creep after a periodof operation. Furthermore, a conical spring 620 may be replaced oradjusted without having to disassemble the rotor and/or windings. Thismakes it significantly simpler to adjust the compressive loading on theradial lead seal assembly 600 on the field, in comparison to theconfiguration described in FIG. 2.

According to one aspect of the invention, the modification may includean on field retrofit of the existing configuration described in FIG. 2.The modification does not involve replacing the coil spring 520 andhence may be implemented during field outages without major rotorcomponent removal.

Referring to FIG. 3, a first step of the retrofit method comprisesremoving one or more of the annular sealing elements 510 from theexisting configuration, to define a radial space between the coil spring520 and the radially innermost sealing element 510. In an exemplaryembodiment, the radial space is produced by removing two of the annularsealing elements 510. In a subsequent step, a plurality of conicalsprings 620 are inserted into the radial space. In the illustratedembodiment, two conical springs 620 are shown to be inserted into theradial space between the coil spring 520 and the remaining sealingelements 510. The number of conical springs 620 to be inserted, andcorrespondingly the number of sealing elements 510 removed toaccommodate the same, may be adjusted on field, depending on an amountof compressive loading required.

In a subsequent step, a radially inward compressive load is applied tothe radial lead seal assembly 600 via a loading member, which in thisembodiment comprises a nut 540. The compressive load may be applied byexerting a torque on the nut 540, for example by a spanner. The radiallyinward compressive load applied to the radial lead seal assembly 600 mayfully compresses the coil spring 520 but only partially compresses theconical springs 620. This would allow the conical springs 620 to depressa prescribed amount under the compressive load on the loading member 540to achieve a total amount of deflection and load desired for the radiallead seal assembly 600. A relaxation of the radial lead seal assembly600 will be recovered by an expansion of the conical springs 620 withonly a small amount of force lost from the compressive load exerted onthe loading member 540.

According to an embodiment, the partial compression of the conicalsprings 620 may be such as to provide enough travel remaining to accountfor thermal expansion of seal elements 510 without becoming fullycompressed. According to an aspect of the invention, conical springs 620in a radial lead seal assembly 600 remain in a partially compressedstate during operation in order to regulate a mechanical pressure in theradial lead seal assembly 600 caused by centrifugal force and thermalexpansion of seal elements 510 during operation. According to an aspectof the invention, conical springs 620 in a partially compressed statemay provide a static and sustained loading on the radial lead sealassembly 600 at both standstill and speed of operation. Theconfiguration of the modified radial lead seal assembly 600 mayeliminate load loosening when at standstill. According to an embodiment,conical springs 620 in a radial lead seal assembly 600 may be only 50%compressed.

According to an embodiment as illustrated in FIG. 3, a transition spacer640 is disposed annularly around the radial lead 400 between the coilspring 520 and the conical springs 620. The transition spacer 640 mayprovide an interface between the coil spring 520 and the conical springs620 so that the compressive load is evenly applied to the radial leadseal assembly 600 to prevent damage of seal elements 510 caused bystress concentrations from uneven loading.

The dimension of a conical spring 620 in a modified configuration of aradial lead seal assembly 600 may be designed to meet loading anddimensional requirements of the radial lead seal assembly 600. A designfeature of the conical spring 620 is that the conical spring 620 is notable to make contact with an insulated surface of a radial lead 400 atany time during assembly or operation. If this occurs, it is possiblethat the conical spring 620 may damage and/or remove a portion of theinsulation of the radial lead 400 and may allow the radial lead 400 tobecome grounded to a rotor body. The conical spring 620 is designed suchthat a clearance from an outer diameter of the conical spring 620 to aninner diameter of a radial lead chamber 420 is smaller than that of aclearance from an inner diameter of the conical spring 620 to an outerdiameter of the insulation of the radial lead 400. This configurationensures that the conical spring 620 will not be able to contact with theinsulated surface of the radial lead 400 at any time during assembly oroperation.

FIG. 4 illustrates a perspective view of a conical spring 620 accordingto an embodiment. The conical spring 620 has an annular surface 660 withan inner diameter ID and an outer diameter OD. The annular surface 660is conical, whereby the inner diameter ID and outer diameter OD areseparated by an overall height OH of the conical spring 620. The innerdiameter ID may be dimensioned to closely fit the diameter of the radiallead 400. As an example, the inner diameter may be in the range of2.836″ to 2.824″ while the outer diameter OD may be in the range of3.637″ to 3.623″.

In the radial lead seal assembly 600, the conical springs 620 may bestacked in different configurations. Stacking conical springs 620 indifferent configurations make it possible to adjust a partiallycompressed travel of conical springs 620 and thus adjust loading to aradial lead seal assembly 600.

FIG. 5 to FIG. 7 illustrates perspective views of conical springs 620oriented in different configurations. FIG. 5 illustrates a seriesorientation, showing three conical springs 620 being arranged in series.FIG. 6 illustrates a parallel configuration, showing three conicalsprings 620 being arranged in parallel to each other. FIG. 7 illustratesan exemplary combination of series and parallel configurations, showingthree groups of conical springs 620 a, 620 b, and 620 c arranged inseries, wherein each group comprises two conical springs arranged inparallel. The number of conical springs 620 used and their orientationmay be determined based on the amount of compressive loading required,and may be adjusted on the field, for example, during an outage ormaintenance. In the embodiment of FIG. 3, the radial lead seal assembly600 comprises two conical springs 620 oriented in a seriesconfiguration.

The modified configuration of a radial lead seal assembly 600 improvesperformance of an existing configuration of a radial lead seal assembly500 that cannot maintain a sufficient compressive loading to the radiallead seal assembly 500 over a period of operation due to seal creep withthermal and compression set.

Furthermore, the modified configuration of a radial lead seal assembly600 may retain a sustained loading required for sealing a radial lead400 of a generator at both standstill and operation speed even afterseal creep and compression set has occurred.

The illustrated retrofit method can be used for modifying an existingradial lead seal assembly of a generator on the field to eliminate aleakage issues without expensive and time consuming disassembly of amajor rotor component.

The disclosed method and the apparatus may be implemented at differenttypes of power generation applications, such as a nuclear powergeneration application.

Although various embodiments that incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings. The invention is not limited in itsapplication to the exemplary embodiment details of construction and thearrangement of components set forth in the description or illustrated inthe drawings. The invention is capable of other embodiments and of beingpracticed or of being carried out in various ways. Also, it is to beunderstood that the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting. The useof “including,” “comprising,” or “having” and variations thereof hereinis meant to encompass the items listed thereafter and equivalentsthereof as well as additional items. Unless specified or limitedotherwise, the terms “mounted,” “connected,” “supported,” and “coupled”and variations thereof are used broadly and encompass direct andindirect mountings, connections, supports, and couplings. Further,“connected” and “coupled” are not restricted to physical or mechanicalconnections or couplings.

LIST OF REFERENCES

-   100 Rotor-   200 Lead Assembly of a Generator-   300 Axial Lead-   320 Axial Chamber-   400 Radial Lead-   420 Radial Chamber-   500 Existing Configuration of a Radial Lead Seal Assembly-   510 Annular Sealing Elements-   520 Coil Spring-   530 Junction between Radial Lead and Axial Lead-   540 Loading Element-   550 Spacer-   560 Top Washer-   570 Bottom Washer-   600 Modified Configuration of a Radial Lead Seal Assembly-   620 Conical Spring-   640 Transition Spacer-   660 Annual Surface of Conical Spring

1. A retrofit method for modifying a radial lead seal assembly of agenerator, wherein the generator comprises a lead assembly forconducting a field current to a rotor winding, wherein the lead assemblycomprises an axial lead extending within an axial chamber through therotor and a radial lead extending radially outward from the axial leadthrough a radial chamber, wherein the radial lead seal assemblyfluidically seals the radial chamber from the axial chamber, wherein theradial lead seal assembly comprises a plurality of annular sealingelements disposed around the radial lead so as to seal an annular spacebetween the radial lead and the radial chamber, a coil spring disposedannularly around the radial lead between the plurality of sealingelements and a junction between the radial lead and the axial lead, anda loading member, the retrofit method comprising: removing one or moreof the annular sealing elements to define a radial space between theremainder of the sealing elements and the coil spring; inserting aplurality of conical springs in said radial space; and applying aradially inward compressive load on the radial lead seal assembly viathe loading member such that the conical springs are only partiallycompressed, wherein a clearance from an outer diameter of the conicalsprings to an inner diameter of the radial chamber is smaller than aclearance from an inner diameter of the conical springs to an outerdiameter of an insulation of the radial lead so that the conical springsdo not contact with an insulated surface of the radial lead.
 2. Theretrofit method according to claim 1, wherein a transition spacer isdisposed annularly around the radial lead between the coil spring andthe conical springs.
 3. The retrofit method according to claim 1,wherein the compressive load exerted by the loading member fullycompresses the coil spring.
 4. The retrofit method according to claim 1,wherein the loading member comprises a nut engaged to the radial chamberat a radially outer end of the radial lead, and wherein the compressiveload is applied by exerting a torque on the nut.
 5. The retrofit methodaccording to claim 1, wherein the plurality of sealing elements are madeof a material comprising neoprene rubber.
 6. The retrofit methodaccording to claim 1, wherein the conical springs are oriented in aseries configuration.
 7. The retrofit method according to claim 1,wherein the conical springs are oriented in a parallel configuration. 8.The retrofit method according to claim 1, wherein the conical springsare oriented in a combination of series and parallel configurations. 9.A radial lead seal assembly of a generator, wherein the generatorcomprises a lead assembly for conducting a field current to a rotorwinding, wherein the lead assembly comprises an axial lead extendingwithin an axial chamber through the rotor and a radial lead extendingradially outward from the axial lead through a radial chamber, theradial lead seal assembly comprising: a plurality of annular sealingelements disposed around the radial lead to seal an annular spacebetween the radial lead and the radial chamber and thereby seal theaxial chamber fluidically from the radial chamber; a coil springdisposed annularly around the radial lead between the plurality ofsealing elements and a junction between the radial lead and the axiallead; a plurality of conical springs disposed annularly around theradial lead in a radial gap between the plurality of sealing elementsand the coil spring; and a loading member for exerting a compressiveload on the radial lead seal assembly in radially inward direction suchthat the conical springs are only partially compressed, wherein aclearance from an outer diameter of the conical springs to an innerdiameter of the radial chamber is smaller than a clearance from an innerdiameter of the conical springs to an outer diameter of an insulation ofthe radial lead so that the conical springs do not contact with aninsulated surface of the radial lead.
 10. The radial lead seal assemblyaccording to claim 9, further comprising a transition spacer disposedannularly around the radial lead between the coil spring and the conicalsprings.
 11. The radial lead seal assembly according to claim 9, whereinthe compressive load exerted by the loading member fully compresses thecoil spring.
 12. The radial lead seal assembly according to claim 9,wherein the loading member comprises a nut engaged to the radial chamberat a radially outer end of the radial lead, and wherein the compressiveload is applied by exerting a torque on the nut.
 13. The radial leadseal assembly according to claim 9, wherein the plurality of sealingelements are made of a material comprising neoprene rubber.
 14. Theradial lead seal assembly according to claim 9, wherein the conicalsprings are oriented in a series configuration.
 15. The radial lead sealassembly according to claim 9, wherein the conical springs are orientedin a parallel configuration.
 16. The radial lead seal assembly accordingto claim 9, wherein the conical springs are oriented in a combination ofseries and parallel configurations.